Supervised fire detection and alarm system



Dec.27,1955 W.J.SCHAFER 2,728,904

SUPERVISED FIRE DETECTION AND ALARM SYSTEM Fi led June 29, 1954 2Sheets-Sheet 1 61 X I'M:

INVENTOR.

W\\.L\AM JSQHAFER ATT OKNEYS Dec. 27. 1955 w. J. SCHAFER SUPERVISED FIREDETECTION AND ALARM SYSTEM 2 Sheets-Sheet 2 Filed June 29, 1954INVENTOR. W\LL\AM d. SCHAFER ATTO RNEYS and bearing the same title.

United States Patent Oflice SUPERVISED FIRE DETECTION AND ALARM SYSTEMWilliam Joseph Schafer, Cleveland, Ohio, assignor to Arthur J. Waldorf,Beachwood Village, Ohio Application June 29, 1954, Serial No. 440,009

3 Claims. (Cl. 340-227) This invention relates in general to anelectrically energized system for sensing abnormal conditions oftemperature, and is a continuation-in-part of my copending application,Serial No. 402,745, filed January 7, 1954 More particularly, thisinvention relates to a fire alarm or signalling system having improvedmeans for sensing and signalling the existence of operative defects anddisturbances in the system so that the operative condition of the systemis automatically and continuously supervised.

It is apparent that an automatic fire detection system, which isincapableof functioning properly when the need arises, is worse thanhaving no system at all. The existence of an inoperative automatic. firedetection system on occupied premises gives the occupants a false senseof security which blunts their vigilance and alertness and thus caneasily result in a condition where total reliance is placed in thesystem, with tragic consequences.

It is a primary object of my invention to provide an automatic firedetection system of the character described which is self-supervising,whereby it will detect and indicate any serious condition ofinoperativeness of the system.

Another object of my invention is to provide a fire detection system inwhich said supervision is automatically and continually maintained.

Still another object of my invention is to provide a tire detectionsystem in which the signal indications for tire conditions are distinctfrom the signal conditions resulting from operative defects ordisturbances.

Other objects and advantages of my invention will be apparent during thecourse of the following description.

in the accompanying drawings forming a part of this specification and inwhich like numerals are employed to designate like parts throughout thesame,

Fig. 1 is a schematic wiring diagram of a supervised fire detectionsystem embodying the features of my invcntion.

Fig. 2 is a plan view of a thermal unit which may be utilized in thefire detection system.

Fig. 3 is a view similar to Fig. 2, with the cover of the thermal unitremoved to show the arrangement of the circuit elements.

Fig. 4 is a diagrammatic view showing the operation of the fuse elementwhich is employed in the thermal unit.

Referring more particularly to Fig. l of the drawings, 1 have shown afire detection system which includes 'a source of power supply 10 whichis preferably independent of the usual power supply of the structure tobe protected, and can conveniently be a low voltage dry cell batteryrated, for example, at nine volts.

The system may, for convenience, be considered as consisting of a powercircuit, a detection and control circuit, and the subsidiary signal oralarm circuits, all of which are fully described hereinafter.

The power circuit is connected in series with the battery 10 andincludes a control relay 11, a voltage relay 2,728,904 Patented 27, 1955of current to cause energization of relay 12. It will be understood thatin selecting the resistor to be used,.con-

sideration must be given to the electrical characteristics of the otherpower circuit elements so as to obtain the functional condition,mentioned above. Such selection is within,the knowledge of one skilledin the art. In the illustrative example of Fig. 1, the resistor 13 mayhave a value of 2000'ohms in relation to relay 11 of 50 ohms and relay12 of 2500 ohms.

For clarity of description, the conductors in the power circuit will beidentified as follows: 14 is the bus line from the positive side of thebattery 10; 15 is the bus line from the negative side of the battery; 16is the lead connecting relay 11 to the positive side of battery 10; 17is the conductor connected to the negative side of relay 11; 18 is alead connecting relay 12 to lead 17; 19 is the lead between relay l2 andresistor 13; and 20 is a lead connecting resistor 13 to negative busline 15. v The detection and control circuit is connected across thebattery 10 in series with the relay 11 and in parallel with the relay l2and resistor 13. This circuit includes a Wheatstone bridge connected at21 to lead 17 and connected at 22 to the negative side of the powercircuit. The resistance value of the Wheatstone bridge preventsenergization of the relay 11 through this circuit.

One arm 23 of the bridge includes one coil 24a of a differential relay24, the other coil 24b of the relay being disposed in an arm 25 of thebridge. A third arm 26 includes a resistor 27, a'variable resistance orrheostat 28 and an external alarm relay 29. The fourth arm 30 of thebridge includes one or more thermal detector units 31 (as shown in Fig.3) connected in series with each other and with signal units 32 which,in this example, are lamps 32a, 32b, 32c and 32d.

Each thermal unit 31 is physically located in a specific detection areaof the structure to be protected, and as many thermal units may be usedas are necessary to provide adequate overall protection. Fig. 1illustrates four of such thermal units 31a, 31b, 31c and 31d. The arm 30also includes a fusible link 33.

Each thermal unit includes a resistor 34 connected in series with asecond larger resistor 35 which is, in turn, in series with a fusiblelink 36. The resistor 34 may, for example, have a value of i5 ohms andthe resistor 35 may be 300 ohms. Connected in parallel across eachresistor 35 is a thermo-mechanical fuse or circuit breaker 37, whichwill be described in more detail hereinafter. Each thermal unit is inseries with one of the lamps 32, which are preferably centrally locatedand consolidated on a control panel which is remote from the thermalunits 31.

In addition to the series arrangement of the thermal units 31, analternate parallel circuit is provided in which the units 31 areindividually connected across the bus lines 14 and 15. These parallelcircuits are established by the closing of the normally-open pluralcontacts 11a, 11b, 11c and 11d of relay 11.

A sensitive relay 38 of the galvanometer type is connected across theWheatstone bridge, as at 39 and 40,

' flow in one direction or the other.

7 in the Wheatstone bridge circuit.

amends switch arm 44 which will indicate the condition of balance orunbalance existing in the Wheatstone bridge circuit. .The relay 38 hasdouble contacts 44a and 44b which are engageable by arm 44 in responseto current The pointer 44 is connected to positive conductor 17 by meansof a lead 45. The contact 44a is connected in parallel with relay 12 bymeans of lead 46. The contact 44b is connected to negative bus line 15by means of a lead 47 to provide a shunt circuit across relay 12 andresistor 13.

A second diode 48 is connected across the sensitive relay 38 and alsoconnects with a resistor 49 which is connected across diode 41. V

The foregoing describes the essential elements of the detectionand'control circuit.

The signal or alarm circuits may be designated as an internal alarmcircuit 50, an external alarm circuit 51 and a trouble alarm circuit 52.

The internal alarm circuit 50 includes a bell 53, or other suitableaudible alarm, which may be located in a convenient central location inthe building or structure to be protected. The bell andrelay 29 arecircuit elements of the arm 26 of the Wheatstone bridge. The internalalarm circuit is closed by the relay-actuated contacts 11c and 111 whichserves to energize the bell 53 and relay 29, respectively. During normaloperation, there is insufiicient current flow through the arm 26 tocause actuation of the bell 53 or relay 29.

The external alarm circuit 51 includes any form of signal or indicatorelement, which may be physically remote from the protected structure. Asexemplary of such an element, I have shown a siren 54 which is connectedin series with an independent power supply 55. The circuit includes arelay-actuated switch arm 29a which is normally maintained in openposition, but which closes the circuit when relay 29 is energized.

The trouble alarm circuit 52 is also preferably provided with anindependent power supply 56 which may be a mercury cell or the like, andwhich serves to en-' ergize an audible alarm such as a buzzer 57. Asinglepole single-throw normally open switch 58 is provided in thecircuit. The circuit is closed by a relay-actuated switch arm 12a whichis usually maintained in open position in response to energization ofrelay 12.

Although it is not an electrical element of the trouble alarm circuit52, I have diagrammatically indicated at 59 a drop flag or target whichmay be utilized as a visual indication of deencrgization of the relay 12in a manner well known in the art. The drop flag 59 is useful inrecording the fact that a trouble condition has existed,

even though the condition may have somehow remedied itself and thusreopened the trouble alarm circuit.

The alarm operation of the above-described system is based upon thecreation of a condition of unbalance Therefore, when the system isoperating normally, the Wheatstone bridge is in balance, i. e., theresistance values of the arms 23 and 26 is equal to that of arms 25 and30. The rheostat 28 which may be rated, for example, at -300 ohms, has asufiicient range to permit the system to be adjusted to a balancedcondition so that no current will flow through relay 38, and thereforepointer 44 will lie intermediate the contacts 444 and 44b.

'A main switch 60 is provided in the power circuit, and preferably it isfused as at 61. When switch 60 is closed, current will flow through thepower circuit to energize relay l2 and thus keepswitch arm 12a fromclosing the trouble alarm circuit 52. However,

I the current value in the power circuit is insuflicient to provided bythe lamps 32. In the absence of the alternate parallel thermal unitcircuit previously described.

any failure of the circuit elements of the thermal arm 30 of theWheatstone bridge or of relay 11 would cause the lamps 32 to beextinguished and thus indicate such failure. However, it is desired notonly that the system indicate that a failure has occurred, but also thatit indicate, whenever possible, the approximate locationof the failureas well as its nature or character, so that it can be distinguished froma fire failure. This attribute of the supervised system is bestexplained by describing the operation of the system under the variousconditions to which it may be subjected.

First, I will discuss some of the trouble or failure conditions whichmight occur independently of a firc condition, and which would generallycause the system to be inoperative unless the condition is noted andremedied.

One of the conditions which might occur, is that resulting from acomplete failure of the power supply circuit. This might be caused by abreak in the power circuit lines, such as line 15, for example. Or itmight result from a short circuiting of the battery 10. Or, if acommunity power supply is being used, it may be caused by some externalsource. Upon power supply failure, the voltage relay 12 is deenergized,and the switch arm 12a is thereby released to close the trouble alarmcircuit 52, and cause the buzzer 57 to be energized. At the same time,the flag 59 will drop. As soon as notice has been taken of the buzzer57, the circuit 52 may be opened by means of normally-closed manualswitch 58, as illustrated in Fig. l, to prevent unnecessary depletion ofthe cell 56. It will be noted that the power failure causes no actuationof the, sensitive relay 38. Therefore, an inspection of the position ofthe pointer 44a will clearly show that the trouble does not lie in anarm of the Wheatstone bridge, but elsewhere in the system. If the powerfailure is only temporary or of short duration, thetrouble'alarm'circuit 52 will be opened by the energization of relay 12as soon as the power supply is restored, and the buzzer will besilenced. However, the position of the flag 59 will indicate that atemporary power interruption has occurred.

In the event the battery 10 weakens or deteriorates through age or use,the system will react in the same manner as it does to power failure.The relay 12 may be selected to be inoperative when the power voltagedecreases below a certain percentage of its normal rating. Thus, forexample, when the battery power drops from a normal nine volts to aboutfive volts, the relay 12 will no longer be eliectively energized and thetrouble circuit 52 will be established. In this manner, the eventualfailure of the. battery can be anticipated, and timely replacement canbe made. It is to be noted, however, that the control relay 11 may beselected to be operative at voltage levels which will exist when relay12 and resistance 13 are shunted out of the power circuit (in a mannerto be described more fully hereinafter) so that, in effect, the systemwill still be operative for fire detection even when the trouble circuit52 indicates that the battery 10 needs replacement.

Another form of trouble condition could be caused by a short circuitinthe thermal arm 30 of the Wheatstone bridge, which would eliminatesome of the resistance elements in this arm. Under such circumstances,the cathode of the diode 41- is negative and the diode acts like arelatively low resistance permitting current to flow through relay 38and cause deflection of pointer 44 toward contact 44a. When-the contactsare closed, a shunt circuit is established across relay 12 which shortcircuits the relay and causes it to become inoperative. This, in turn,causes the trouble circuit 52to be established in the manner previouslydescribed. After the short circuit is found and remedied, the pointer 44is reset to its neutral position and the relay 12 will then becomeenergized to cause the trouble alarm circuit 52 to be opened. Theshunting effect of diode 48 on sensitive relay 38 is negligible due tothe relatively low resistance of the relay 38.

When there is a break in the alarm arm 26 of the circuit, the anode ofthe diode 41 becomes positive and the system reacts in the same manneras it does to a shortcircuit in the thermal arm 30.

Another trouble condition may occur when there is a break in the thermalarm 30. This causes the cathode of diode 41 to go positive thus causingit to become nonconducting. However, some current will flow through theparallel resistor 49 and this will cause a very slow movement of pointer44 toward contact 441). At the same time, the open thermal arm willcause effective elimination of the bucking fiux of the coil 24b of thedifferential relay 24 which holds contact arm 24c against contact 42.The arm 240 is thereby actuated to make contact with a contact lead 42awhich connects diode 41 with the negative side of the power supplythrough a high resistance 62 which is provided to prevent a dangerouslevel of current flow through the sensitive relay 38. The diode thenwill permit current to flow through relay 38 to cause the pointer arm 44to swing in the opposite direction and make contact with 44a beforethere has been time for it to make contact with 44b. The relay 12 isthus shorted out and the circuit 52 is established to visually andaudibly indicate the existence of the difficulty.

The foregoing represents the principal trouble conditions which aredetected by the system, and which are indicated by a signal which isdistinct from the alarm which is given when a fire condition exists, sothat there should be no undue panic due to false alarms.

If an uncontrolled fire condition should develop in any area which issupervised by a thermal unit 31, the increase in ambient temperaturewill cause the fuse element 37 to open. As best seen in Fig. 4, theelement 3'7 includes three sections 37a, 37b and 37c which are joined orbonded to each other at their terminal junctures 63, 64 by a low-meltingfuse metal 370'. The sections 37a and 372; which are each connected tothe resistor 35 are made of electro-conductive material whichinterruption oriailure of the circuit established by the pointer arm 44and contact 44b.

The actuation of the contacts 1la--11d establishes the parallel thermalunit circuits 31a-31d, previously described. If, for example, the fuseelement 37 of thermal unit 310 has opencd,'the lamp 320 will besubstantially extinguished. However, the remaining lamps 32a, 32b and32d will be in parallel and will be lit. Thus, the affected area can bedetermined quickly.

The closing of contacts lie and 11 causes internal alarm circuit to beenergized and causes bell 53 to sound. The energization of relay 29closes the external alarm circuit 51 and causes the siren 54 to beactuated.

The short-circuiting of the relay 12 also causes the trouble circuit 52to be established. Thus a fire condition will cause two separateindependently powered alarm circuits to be activated, in addition to thetrouble circuit 52. This condition (fire) is thus clearly and readilydistinguished from the various trouble conditions.

The actuation of control relay 11 causes a momentary polarized voltagesurge which tends to swing pointer 44 away from contact 44b. By placingthe diode 48 in parallel with the relay 38, the diode absorbs the bulkof the surge and prevents the breaking of the connection with contact441).

A manually operable sequential push-button switch 65 is provided fortesting the external alarm circuit 51 and relay 29, as well as servingas a manual burglar alarm system or the like. One set of contacts 650',short-circuits the relay contact 11f and serves to close the circuit torelay 29. A second set of switch contacts 65b short is pre-stressedduring the assembly so as to cause the sections 37a and 37b to divergeat points 63 and 64 when the fuse metal becomes plastic or melts. Theintermedi ate section 370 is also 'electro-conductive and is prestressedduring assembly so that its arms will converge toward each other whenthe fuse metal 37d becomes plastic. This arrangement provides a snapaction fuse element which is not subject to the vagaries which areencountered in using a simple fusible link, such as 36, and whichtherefore responds more efiiciently and more precisely to thetemperature condition to which it has been calibrated. However, fusiblelink 36 is retained in the circuit as an additional safeguard.

The fuse element 37 which normally short-circuits a resistor 35, causesthe resistor 35 to be placed in series in the thermal circuit whenever afuse element 37 opens, and thus adds about 300 ohms of resistance to thethermal arm 30. This increase in resistance causes the cathode of diode41 to become positive and the diode becomes non-conductive. The currentthen flows through resistance 49 and relay 38, in the manner heretoforedescribed, to cause pointer arm 44 to swing slowly toward contact 44b.In this instance, however, the increased resistance of the thermal arm30 is not of great enough magnitude (as distinguished from the opencondition) to 'cause actuation of contact arm 24c of differential relay24. I

When contact 441; is made, a short-circuit is established across relay1?; and resistor 13. The elimination of the resistance of the elements12 and 13 from the power circuit causes actuation of control relay 11 toclose the multiple contacts Ila-41f, previously described, as well as acontact 11g which serves to assure continued energization of relay 11even if there should be a subsequent circuits the relay 38 and diodes inthe Wheatstone bridge to prevent any actuation of the relay 38. Theswitch 65 is designed to close the contacts 65b before closing thecontacts 65a.

From the foregoing it will be apparent that I have provided a supervisedfire detection system which normally is in a condition of electricalbalance. When the balance is destroyed by a moderate decrease inresistance in the thermal arm of the system or by an infinite increase(break) in the resistance of the thermal arm or alarm arm, a troublealarm circuit will be actuated. However, a moderate increase in theresistance of the thermal arm will establish independent and distinctivelocal and re mote alarm bircuits in addition to the trouble alarmcircuits, so that a fire condition is clearly emphasized anddistinguished from a trouble condition.

Additionally, means have been provided for safeguarding continuedoperation of the control relay after a fire condition has been detected,and means have also been provided for testing or operating an externalsignal or alarm independently of the other circuit-s and withoutdisturbing them.

In Figs. 2 and 3 I have shown a form of thermal detector unit 31 whichmay be utilized in the system herein described. The thermal unit 31includes a base 66 which is adapted to be secured to a surface, such asa wall or ceiling, by means of fasteners 67. The base 66 is preferablymolded of a rigid synthetic resin and has integrally formed thereon acentrally projecting stud 68. An aperture 69 is provided in the base forpassage of the conductor wires or cable.

A circular cover 70, also preferably formed of molded synthetic resin,is threadedly secured to the stud 68. The cover is provided with anannular flange 71 having a larger diameter than the base 66, so that anunobstructed annular space 72 is provided for circulation of air.

Secured to terminal posts 73 on the base, are the resistor 34 in serieswith link 36 and with fuse element 37 which is connected in parallelwith resistor 35. Conductor wires 74 serve to connect the thermal unit31 with the other circuit elements of the system.

The cover prevents foreign articles or particles from accidentallyinjuring the elements of the thermal unit circulation of air It will beunderstood that all the components of the system, except the thermalunits 31 and the external alarm 54, may be physically grouped in acentral control box or the like. The lamps 32 may be associated withsuitable indicia of area location.

It is to be understood that the form of my invention, herewith shown anddescribed, is to be taken as a preferred example of the same, and thatvarious changes in the shape, size and arrangement of parts may beresorted to, without departing from the spirit of my invention, or thescope of the subjoined claims.

Having thus described my invention, I claim:

1. In a fire detection system of the character described, thecombination of an electrical power supply, a balanced resistance circuitconnected to said power supply, an alarm element in one arm of saidcircuit, a first switch means for connecting said alarm element directlyto said power supply, a thermo-responsive detection unit in an opposedarm of said circuit, a sensitive relay in said circuit energizable inresponse to a condition of unbalance resulting from a change in theresistance value of either of said arms of said circuit, a control relayin series with said balance resistance circuit and actuated in responseto a current value greater than that of said circuit, and a secondswitch means responsive to actuation of said sensitive relay forconnecting said control relay directly to said power supply foractuating said control relay, said first switch means being responsiveto actuation of said control relay to actuate said alarm element.

2. In a fire detection system of the character described, thecombination of an electrical power supply, a balanced resistance circuitconnected to said power supply, an alarm element in one arm of saidcircuit, an external alarm relay in said arm of said circuit, athermo-responsive detection unit inan opposed arm of said circuit, acontrol relay in series with said balanced circuit, said balancedcircuit depressing the current flow through said control relay and saidalarm element and said external alarm relay to an inoperative value, anormally-open external alarm circuit, switch means responsive toactuation of said external alarm relay for closing said external alarmcircuit, means responsive'to a condition of unbalance in said circuitfor actuating said control relay, and switch means responsive toactuation of said control relay for actuating said alarm element andsaid external alarm relay.

3. In a fire detection system of the character described,

the combination of an electrical power supply, a nor-" mally balancedWheatstone bridge connected in series with said power supply, athermo-responsive detection unit in one arm of said bridge, adirectional relay connected across said bridge and energizable inresponse to a condition of unbalance in said bridge, a trouble alarmcircuit, first switch means responsive to one direction of current flowthrough said relay for actuating said trouble alarm circuit, anormally-open fire alarm circuit, second switch means responsive to anopposite direction of current flow through said relay for establishingsaid fire alarm circuit, means for causing current fiow in said onedirection in response to a decrease in the electrical resistance of saidthermo-responsive detection unit, means for causing current flow in saidopposite direction in response to an increase in the electricalresistance of said thermo-responsive detection unit, means for reversingsaid current flow in said opposite direction in response to an infiniteincrease in the electrical resistance of said thermoresponsive detectionunit, and means provided in said thermo-responsive detection for addingelectrical resistance to said unit in response to a predetermined valueof temperature.

References Cited in the file of this patent UNITED STATES PATENTS311,681 Sawyer Feb. 3, 1885 1,008,482 Lovejoy Nov. 14, 1911 2,074,262Grant Mar. 16, 1937 2,094,211 Grant Sept. 28, 1937

